It is well known that peroxygen bleaches are effective in removing stains and/or soils, as well as visible evidence of stains and/or soils, from textiles and fabrics. Unlike sodium hypochlorite bleaching solution, they can be readily employed in a variety of bleaching and detergent compositions. However, the efficacy of peroxygen bleaches can vary greatly with temperature. These bleaches are only practicable and/or effective when the bleaching solution (bleach and water mixture) is above about 60.degree. C. When employed in a bleach solution at a temperature of about 60.degree. C., or below, peroxygen bleaches are significantly less efficacious than at higher temperatures. Therefore, to obtain a desirable level of bleaching performance at these lower temperatures, extremely high levels of peroxygen bleach must be employed. Due to the cost of peroxygen bleach compounds, levels necessary to achieve good bleaching performance at such temperatures are economically impracticable. In bleach solutions where the temperature during use is well below 60.degree. C., peroxygen bleaches are rendered almost totally ineffective regardless of the level of peroxygen bleach compound added to the system.
The dependence of peroxygen bleach performance on temperature (and concentration), described above, is both practically and economically significant. Peroxygen bleaches are most commonly used as detergent adjuvants in home laundry products. Thus, the typical textile wash process employing these bleaches utilizes an automatic household washing machine and a wash-water temperature below 60.degree. C. As a consequence, there has been much interest in developing substances that would increase the efficacy of peroxygen bleach compounds allowing them to be effectively employed at a temperature below 60.degree. C. and especially at temperatures less than about 35.degree. C., typically used in hand-washing. Such substances are generally referred to in the art as bleach activators or peroxygen bleach activators.
Most of these prior art bleach activators are granular in character and are intended primarily as adjuncts to conventional laundry detergent granules. Such bleach activator granules conventionally comprise a bleach activator in admixture with a coating or carder material which serves to enhance the stability of the bleach activator and facilitates its uniform dispersion in the granular laundry detergent.
One such class of bleach activators which have been found to provide good bleaching of textiles and fabrics are the acyl lactam bleach activators, such as benzoyl caprolactam and benzoyl valerolactam. However, slow solubilizing lactam bleach activators such a benzoyl caprolactam can be difficult to use in granular laundry detergent compositions because they tend not to, solubilize/disperse satisfactorily in the wash water, especially at low wash water temperatures. The unsolubilized bleach activators may fail to be convened to peracids or precipitate on the fabrics in the wash where they then react with the peroxygen bleach and many times spot or remove color from the fabrics.
Still another problem in the manufacture of stable, soluble acyl lactam bleach activator particles is the relatively low melting point of some activators. Typically, methods for making bleach activator particles involve the use of water to form a mixture of the bleach activator with the other granule additives. After the granule additives and activator have been adequately combined, excess water must be removed, usually by some form of heat-assisted drying. Such drying processes for making acyl lactam bleach activators-containing particles are frequently inefficient because they require temperatures below the melting point of the bleach activators to preserve particle form and functionality.
The use of a liquid or molten surfactant intimately mixed with the bleach activator would seem to avoid the need for water in the process. However, because of the relatively low melting point of the acyl lactam activators, the choice of a suitable surfactant is limited. The surfactant should improve solubility of the activator. The surfactant should also allow the final granular product to be solid and non-sticky at room temperature (.about.20.degree.-25.degree. C.) and/or while the laundry product, which comprises the activator particle, is in storage where temperatures can reach 50.degree.-55.degree. C.
The present invention seeks, as one of its objectives, to resolve the problems of utilizing acyl lactam bleach activators in granule form by providing a stable matrix of materials in a particulate form that has satisfactory rate of solution/dispersibility and perhydrolysis characteristics, especially in cool wash water. The invention further seeks to provide a process which does not involve a drying step. Also, the invention seeks to provide bleach activator particles which are suitable for admixing into detergent formulations, i.e., they are non-sticky, have low friability and are free flowing.